Automatic control system



Aug. 12, 1958 IT 2,847,166

AUTOMATIC CONTROL SYSTEM Filed Sept. 6, 1955 INVENTOR. JAMES L. SMITH Wi t/79 W ATTORNEYS United States Patent 2,847,166 AUTOMATIC CONTROL SYSTEM James L. Smith, Philadelphia, Pa. Application September 6, 1955, Serial No. 532,807 3 Claims. (Cl. 236-91) (Granted under Title 35, U. S. Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates to automatic control systems and in particular is concerned with maintaining constant heat transfer between two fluids such as a cooling liquid bath and another liquid material which is to be cooled.

Difiiculty has been experienced in pumping fuel oil which has been in storage at low temperatures and studies of the fiowability of oil at low temperatures shows that its behavior deviates from that which would be expected of such material. These deviations are believed due to the prior practices of preparing or treating the oil samples. It is customary to rapidly solidify the oil samples, but this procedure is usually accompanied by wax crystal formation and it is believed that the formation is a result of the uncontrolled rate of cooling. In a standard procedure for measuring the fluidity or pour point of an oil sample the oil is cooled to a physical state where no movement is observed when the sample in a vessel is inclined or tilted, the cooling being accomplished by placing the oil sample in a freezing bath at a fixed temperature. The cooling rate is at first rapid, but decreases as the oil temperature approaches the bath temperature.

The principal object of the invention is directed to an arrangement for regulating heat transfer between two fluids in accordance with pressure differential between the fluids.

A more specific object is to provide for the constant rate of heat transfer between a liquid sample and a liquid bath by the pressure differences existing in the liquids.

Other objects and advantages of the invention will hereinafter become more fully apparent from the following description of the annexed drawing.

Referring to the single figure of the drawing, which shows the apparatus generally diagrammatically with parts in section, the numeral 10 indicates a vessel providing a liquid bath and containing brine, alcohol, water, etc. Within the vessel 10 is disposed a receptacle 12 containing a sample of oil which is to be analyzed, and the level of the liquid bath and oil sample extends upwardly to a level as indicated at 14.

Air pressure devices 16 and 18 are disposed respectively in the liquid bath and in the sample liquid and, if desired, may be entirely submerged in the liquids. The pressure devices are of suitable size and shape to transmit air therefrom under varying pressure conditions through conduits 20 and 22 each of which has one end in communication with a pressure device, as shown. The conduits 20 and 22 have their other ends in communication respectively with capillary tubes 24 and 26 which are respectively provided with valves or stop cocks 28 and 30 for adjusting or equalizing air pressure in the pressure devices 16 and 18 when the device is set for operation.

The other ends of the tubes 24 and 26 are in communication with a mercury reservoir 32 which is maintained filled with mercury and these tubes extend at a change conduit within said bath, a

slight angle to the horizontal between the conduits 20 and 22 and the reservoir in order that maximum displace ment of mercury from the vessel 32 is effected under slight pressure differences between the pressure devices 16 and 18. A stopper 35 is provided in the reservoir 32 for the purpose of supplying mercury thereto.

A plurality of contact lines each identified by the letter C are disposed in tube 24 and the contact lines are spaced in accordance with selected increments of pressure difference it is desired to maintain between the liquid sample in the vessel 12 and the liquid bath in vessel 10. For example, four contact lines C are shown and these may be spaced so that the mercury from vessel 32 will be transmitted to the contact nearest the vessel 32 when a small pressure differential, as of the order 25 p. s. i., exists between the pressure devices 16 and 18. When a large pressure difference of upwardly of p. s. i. exists between the pressure devices, mercury will be forced into contact with the contact line C which is nearest the valve 28. A movable contactor 34 is provided and may be set in contact with a selected one of the contact lines C in accordance with the temperature difference it is desired to maintain between the sample liquid and the bath liquid.

The temperature difference between the liquid bath and the liquid sample is maintained by pumping a cooling medium from a source 36 by a pump P driven by a motor M. The motor M is arranged in an electrical circuit so that pump P operates until it is deenergized at the time a selected temperature difference exists between the sample liquid and the liquid bath. To this end, the motor M is in circuit between power lines X and Y through a switch S which is normally closed and the motor is inoperative when the switch is opened.

Switch S is part of a relay R which is controlled by an independent circuit including battery B, the movable contact arm 34 and a selected one of the contact lines C. The switch S is actuated to open position when the mercury in transmitting tube 24 completes the circuit to the selected one of contact lines C and energizes solenoid E to cut off power to the motor M.

As the temperature of the liquid in the bath 10 drops when coolant is circulated through heat exchanger 38, the pressure in pressure device 16 is reduced and as heat is transferred from the sample to the bath the pressure differential between the device 16 and the device 18 is reduced and the motor M will continue in operation until the pressure diiference forces the mercury upwardly in the tube 24 from the mercury reservoir 32 to the selected contact line C which becomes energized and operates solenoid E through movable contact 34.

In the reverse situation, when a heated medium is used to heat the bath liquid, it would be necessary only to reverse the position of the pressure devices by placing the device 16 within the vessel 12 and have the mercury displaced by the device 18 in accordance with pressure increase in the liquid bath in the vessel 10.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

l. A control system for maintaining a substantially constant temperature difference between a liquid bath and a liquid specimen disposed within said bath in heat exchange relation therewith which comprises a heat exheat exchange fluid reservoir and a motor operated pump, said heat exchange conduit having one end in communication with the reservoir and its other end in communication with the pump for circulating a fluid in heat exchange relation with said liquid bath, a first pressure device in the liquid bath 3 having a first pressureline extending therefrom, a second pressure device in the liquid specimen having a second pressure line extending therefrom, a transmitting fluid reservoir, a first transmitting line between the reservoir and the first pressure line, a second transmitting line between the reservoir and the second pressure line, contact means in one of the transmitting lines, a power source and a normally closed switch in circuit with said motor operated pump for circulating the heat exchange fluid through the heat exchange conduit, a manual selector arm in circuit with said contactor means, a solenoid in circuit between the fluid in the transmitting fluid reservoir and the manual selector arm, said solenoid being operable to open said switch and stop circulation of the heat exchange fluid when the temperature difference between the bath and the specimen forces the transmitting fluid upwardly in said one transmitting line to the contactor means.

2. A control system for maintaining a substantially constant temperature difference between a liquid bath and a liquid specimen disposed within said bath in heat exchange relation therewith which comprises a heat exchange conduit within said bath, a heat exchange fluid reservoir and a motor operated pump, said heat exchange conduit having one end in communication with the reservoir and its other end in communication with the pump for circulating a fluid in heat exchange relation with said liquid bath a first pressure device in the liquid bath hav ing a first pressure line extending upwardly therefrom, a second pressure device in the liquid specimen having a second pressure line extending upwardly therefrom, a transmitting fluid reservoir disposed in a horizontal plane above the bath and between said pressure lines, a first transmitting line between the reservoir and the first pressure line, a second transmitting line between the reservoir and the second pressure line, a group of spaced contactors in one of the transmitting lines, a power source and a normally closed switch in circuit with said motor operated pump for circulating the heat exchange fluid through the heat exchange conduit, a manual selector arm in circuit with one of said contactors, a solenoid in circuit between the fluid in the transmitting fluid reservoir and the manual selector arm, said solenoid being operable to open said switch and stop circulation of the heat exchange fluid when the temperature difference between the bath and the specimen forces the transmitting fluid upwardly in said one transmitting line to said one contactor.

3. A control system for maintaining a substantially constant temperature difference between a liquid bath and a liquid specimen disposed within said bath in heat exchange relation therewith which comprises a heat exchange conduit within said bath, a heat exchange fluid reservoir and a motor operated pump, said heat exchange conduit having one end in communication with the reservoir and its other end in communication with the pump for circulating a fluid in heat exchange relation with said liquid bath a first pressure device in the liquid bath having a first pressure line extending upwardly therefrom, a second pressure device in the liquid specimen having a second pressure line extending upwardly therefrom, a transmitting fluid reservoir disposed in a horizontal plane above the bath and between the pressure lines, a first transmitting line extending at an angle upwardly between the reservoir and one of said pressure lines, a second transmitting line between the reservoir and the other pressure line, a group of spaced contactors in the first transmitting line, a power source and a normally closed switch in circuit with said motor operated pump for circulating the heat exchange fluid through the conduit, a selector arm in circuit with said switch and manually movable to a selected contactor, a solenoid in circuit between the fluid in the transmitting fluid reservoir and the manual selector arm, said solenoid being operable to open said switch and stop circulation of the heat exchange fluid when the temperature ditference between the bath and the specimen forces the transmitting fluid upwardly in said first transmitting line to the selected contactor.

Ray June 28, 1949 Brown et al. July 14, 1953 

